1. Field of the Art
This invention relates to an air conditioning system for cooling or heating a room in a vehicle, house or the like, and more particularly to an air conditioning system which is capable of correctly detecting the amount of residual coolant.
2. Technical Background
The air conditioners are generally arranged in the manner as shown in FIG. 6. In this particular example of the prior art, the air conditioning system is shown as being mounted on a vehicle.
In FIG. 6, the reference 1 denotes the piping which defines circulation passages for a coolant such as ammonia gas, flon gas or the like. Successively provided along the length of the piping 1 in the direction of circulation of the coolant (in the direction of arrow A) are a compressor 2, a heat radiator 3, a coolant storage tank 4, an expansion valve 5 and a heat absorber 6. The compressor 2, heat radiator 3, coolant storage tank 4 and expansion valve 5 are located in an engine room (not shown), while the heat absorber 6 is located in a passenger's room (not shown).
With the above arrangement, the coolant which is compressed in gas phase at the compressor 2 turns into liquid phase by releasing heat at the heat radiator 3. The coolant is then circulated to the expansion valve 5 through the coolant storage tank 4 to undergo pressure reduction, and turned into gas phase by heat absorption at the heat absorber 6 before flowing into the compressor 2. As a result of a series of these actions, the coolant cools the passenger room of the vehicle by absorbing heat at the heat absorber 6 and releasing heat to the outside of the vehicle at the heat radiator 3.
On the other hand, in many cases the coolant which is sealed in the system escapes to the outside during use over a long period of time, inviting such reductions in the amount of residual coolant as will deteriorate the functions of the air conditioning system to a material degree.
Therefore, it becomes necessary to check the amount of residual coolant and, for this purpose, there have thus far been introduced various measures including a checkup window provided in an upper end portion of the coolant storage tank and a pressure sensor provided in a liquid phase region upstream of the expansion valve 5 to detect variations in pressure resulting from decreases of the coolant in the system. In case of the pressure sensor, an alert device which is provided in the passenger's room of a vehicle is actuated by a signal from the pressure sensor upon detection of a deficiency of residual coolant, in order to notify the driver of the deficiency.
In case a checkup window alone is provided as a residual coolant sensor means in the above-mentioned prior art, it is necessary to inspect the condition of the residual coolant periodically through the checkup window despite the troublesomeness of the inspection job.
Further, in case of the pressure sensor, there arises a problem of inferior accuracy in detecting the amount of residual coolant because the pressure sensor is located in a liquid phase region which is pressurized by the compressor 2, so that there occur no great changes in pressure from the liquid to gas phase.
With the foregoing problems in view, the present inventor conceived of detecting the amount of residual coolant by the use of a self-heated type thermistor, conducted research including measurement of variations in the resistance of a self-heated type thermistor inserted in the piping which defines flow passages for the coolant.
However, in this instance the self-heated type thermistor is held in direct contact with the coolant, so that it is likely to be cooled to an excessive degree depending upon the coolant flows. Besides, the flow velocity of the coolant is increased in the gas phase by reduced flow resistance and its cooling effect becomes higher in proportion to the increased flow velocity, and consequently the resistance which is proportional to the temperature variation does not change greatly from liquid phase to gas phase.
In view of the foregoing unsolved problems, it is an object of the present invention to provide an air conditioning system which is capable of correctly detecting leaks and deficiency of the coolant in a simplified manner.